1. Technical Field
The present invention relates to a coefficient decision apparatus, a radio communication system, a coefficient decision method, and a memory medium which stores a coefficient decision program, and in particular, to a coefficient decision apparatus, a radio communication system, a coefficient decision method, and a memory medium which stores a coefficient decision program, which can decide a filter coefficient used at the time of averaging a transmission power value.
2. Background Art
In a common radio communication system, while a radio terminal moves freely between cells, radio communication is performed. For this reason, in a radio base station where many radio terminals exist in a cell, electric power energy may increase and a congestion state may arise. When a congestion state arises, various problems, such as a transit delay, quality degradation, and line disconnection, will arise.
For these reasons, when a congestion state arises, communication control of restricting a new call and the like is performed and various kinds of congestion control methods for resolving the congestion state are proposed.
For example, in Patent Document 1 (Japanese Patent Laid Open Publication No. 2005-210189), a radio base station controller starts congestion control when receiving a congestion occurrence notice from a radio base station. In addition, a technique of releasing congestion control at the time when a radio base station controller receives a congestion dissolution notice from a radio base station is disclosed.
In addition, Patent Document 2 (Japanese Patent Laid Open Publication No. 2006-135516) discloses a technique of judging an ATM (Asynchronous Transfer Mode) cell is congested when a predetermined frequency or more of discard of ATM cells arise, and restricting registration of a new call.
Furthermore, Patent Document 3 (Japanese Patent Laid Open Publication No. 2002-238073) discloses a technique of averaging measurements of a transmission power level, and regarding the averaged value to be a criterion to perform a call reception judgment.
Here, a congestion control method (a first method) used in a radio communication system will be described with referring to FIG. 23. FIG. 23 is a schematic diagram at the time of a radio network control station detecting a congestion state. A horizontal axis of FIG. 23 denotes the time, and a vertical axis denotes the electric power value. The radio network control station is a controller which controls a radio base station.
First, a radio network control station acquires an “electric power instantaneous value” (a transmission power value of a radio base station), which a radio base station measured for the unit of its cell, from radio base stations, as shown in FIG. 23.
Next, the radio network control station compares the “electric power instantaneous value” acquired from the radio base station with a “congestion control threshold” (value acting as a criterion of judgment for deciding whether a congestion arose or not), as shown in FIG. 23.
Then, as shown in FIG. 23, when the “electric power instantaneous value” exceeds the “congestion control threshold”, the radio network control station judges that the power capacity of the radio base station reaches a limit value, starts congestion control to the radio base station, and controls communication with the radio base station and radio terminals.
Thereby, the radio network control station can perform congestion control to the radio base station on the basis of the “electric power instantaneous value.”
However, as shown in FIG. 23, in the first method mentioned above, even in a state that the “electric power mean value” (value obtained by averaging the electric power instantaneous value) is lower than the “congestion control threshold” and power capacity of the radio base station still has a margin, when the “electric power instantaneous value” exceeds the “congestion control threshold”, congestion control is started.
For this reason, when a situation that the “electric power instantaneous value” exceeds the “congestion control threshold” temporarily arises, the first method mentioned above cannot use the power capacity of the radio base station effectively. As the situation where the electric power instantaneous value exceeds the congestion control threshold temporarily, for example, an increase in momentary traffic, power variation of a radio terminal, etc. are mentioned.
In recent years, data transmission services have spread and it is supposed that an electric power instantaneous value fluctuates in burst by burst property of data communication. For this reason, as shown in FIG. 23, it is supposed that a situation that an “electric power instantaneous value” exceeds the “congestion control threshold” temporarily arises further easily.
Methods for using effectively power capacity of a radio base station include the following methods (a second method), for example.
First, an increase and decrease trend of an electric power instantaneous value is investigated, and a future electric power instantaneous value is estimated on the basis of a result of the investigation.
Then, when the future electric power instantaneous value (estimated electric power instantaneous value) and congestion control threshold are compared and the estimated electric power instantaneous value exceeds the congestion control threshold, it is judged that the power capacity of the radio base station will reach a limit value in the future, and it is controlled to increase a radio base station.
Thereby, since it is not necessary to perform the first method shown in FIG. 23 mentioned above, it becomes possible to use the power capacity of the radio base station effectively.
However, the second method mentioned above needs to investigate the increase and decrease trend of an electric power instantaneous value for a long period of time (for example, several weeks), and in order to estimate an estimated electric power instantaneous value, it will require most time.
In addition, since an increase and decrease range of an electric power instantaneous value is large, it becomes difficult to estimate an estimated electric power instantaneous value correctly.
In consequence, although the power capacity of a radio base station still has a margin, an excessive radio base station may be increased and a case that equipment cost is made to increase may arise.
In addition, although there is no margin in power capacity of a radio base station, a radio base station is not increased, but in consequence, radio wave interference increases and degradation of communication quality may be caused.
Methods for using effectively power capacity of a radio base station include the following methods (a third method), for example.
First, a radio network control station acquires an electric power instantaneous value, which a radio base station measured for the unit of its cell, from radio base stations.
Next, the radio network control station averages the electric power instantaneous values collected from each of the radio base stations using each filter coefficient, calculates each electric power mean value (value obtained by averaging the electric power instantaneous value), and compares each calculated electric power mean value with a congestion control threshold.
Then, when the electric power mean value exceeds the congestion control threshold, the radio network control station judges that the power capacity of the radio base station reaches a limit value, starts congestion control to the radio base station, and controls communication with the radio base station and radio terminals. The filter coefficient is used when calculating an electric power mean value.
Thereby, since the radio network control station performs the congestion control when an electric power mean value exceeds the congestion control threshold, it becomes possible to use the power capacity of the radio base station effectively.
However, an actual condition is that there is no standard for deciding the filter coefficient used by the third method mentioned above when calculating an electric power mean value.
For this reason, in a present system, in order to decide a filter coefficient, communication is interrupted temporarily, and complicated operations of deciding a most suitable filter coefficient are done with changing setting of a filter coefficient for the unit of its cell.
Hence, in the third method mentioned above, operating expenses in connection with deciding a most suitable filter coefficient, and a profit loss in connection with a temporary interruption of communication arise.
In consequence, the expenses accompanying a setting change of a filter coefficient becomes larger than applying the third method mentioned above to use the power capacity of radio base stations effectively.
Hence, it becomes necessary to develop a method of deciding efficiently a filter coefficient used when calculating an electric power mean value.
In addition, the above-mentioned Patent Documents 1 and 2 disclose techniques for resolving a congestion state when the congestion state arises.
Furthermore, the Patent Document 3 discloses a technique of averaging measured values of a transmission power level, and regarding the averaged value to be a criterion to perform a call reception judgment.
However, the above-mentioned Patent Documents 1 to 3 do not describe a specific solution for deciding efficiently a filter coefficient used for averaging the transmission power value, and do not suggest its necessity at all.
For this reason, it is not possible by the techniques of the above-mentioned Patent Documents 1 to 3 not only to decide a filter coefficient used for averaging the transmission power value efficiently, but also to aim at further effective use of power capacity of radio base stations.